This invention relates to the method of manufacturing a lens for use in an aircraft, such as a lens cover for a navigation light that may typically be placed at an aircraft wing tip. Lenses for use in aircraft have three demanding basic requirements. First, the lens must be exceedingly strong to sustain the impact from hail, foreign objects, etc. and thermal shock to which a lens on an aircraft is subjected, especially to which a lens on a modern high-speed jet aircraft is subjected. Second, an aircraft lens typically is of a complex configuration to meet the aerodynamic requirements of an aircraft exterior design. A third requirement is that the lens must be highly transparent to permit a substantial portion of light from a light source to pass therethrough and therefore must resist the erosion effects of ice crystals, sand and rain.
Lenses for aircraft application are typically manufactured of plastic material, such as polycarbonate, acrylic or the like. A lens is made by first forming a pattern in a sheet of base translucent material. The pattern, after being cut to its prescribed dimensions in the form of a flat blank member, is then molded, formed and contoured into the desired ultimate configuration. After the configuration of the lens is formed, the edge is finished to match the requirements of the lens to fit in its location within a lens receptacle of an aircraft.
Since aircraft lenses typically must be formed in contoured aerodynamic shapes, there is a tendency to develop stress in the edge of the lenses when the lenses are mounted to an aircraft, and failure of aircraft lenses typically begins with cracks forming in an edge of the structure.
The main objective of this disclosure is to provide an improved method of manufacturing a lens for use on an aircraft that resists erosion from hail, sleet, sand and the like and that also resists cracks, from thermal excursions, originating at the lens edge.